Isothermal cover with thermal reservoirs



United States Patent [1113,548,930

[ Inventor Byrd 3,152,774 10/1964 Wyatt 244/1 3,450,195 6/1969 Schnacke 165/ 105X gig. Nomgzf 3,490,718 1/1910 Vary mas/105x l C 9 [45] Patented Dec. 22, 1970 OTIIFER REFRENCE [73] Assign mum sum America as Katzoff S., Proceedlngs of Joint 1Mom1c Energy Comm1ss1on/Sandra Laboratones Heat P1pe Conference, Space represented by the Administrator of the l v 1 NM AM I'd 8pm sotope Power Department, Sand1a Laboratories, 0]. Oct., Admhmm 1966 pp 72 to 74 (more fische) Primary Examiner-Albert W. Davis, Jr. Attorneys-L. D. Wofford, Jr., G. 1. Porter and G. T. Mc Coy ABSTRACT: An isothermal cover for a spacecraft. The [54] COVER wrm THERMAL device is a double-walled cylinder enclosing a number of con- CHI", 4 Mb m tainers of fusible material, mounted on struts inside the walls of the cylinder, for use as heat reservoirs. The inside surfaces [52] US. (L 165/105, of the cylinder and the outside surfaces of the containers and 165/ 165/ l 33, 7 219/530 struts are covered with a wicking material. The struts may also [51] Int. Cl. F28d /00 be fabricated solely of the wicking material. The cavity of the Field Search /105, double-walled cylinder also contains a heat transfer fluid, The 540 device functions as a heat pipe in transferring heat from its sunlit to its other (dark) side. The heat reservoirs store heat [56] RM CM when the device is in sunlight and return the heat to the system UNITED STATES PATENTS when the device is in darkness. Electrical heaters also furnish 2,342,211 2/1944 Newton 165/105X heat to the system if needed to keep the system at constant 2,825,034 2/1958 Birchard 165/104X temperature.

PATENTED B8322 I978 FIG FIG.3

INVENTOR AMBROSE W. BYRD ATTORNE YS ISOTHERMAL COVER WITH THERMAL RESERVOIRS ORIGIN OF THE INVENTION A The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION 1. Field of the Invention v The invention relates to equipment covers and more particularly to a constant-temperature isothermal cover for a spacecraft.

2.Description of the Prior Art The technical fields of heating and refrigeration are old established fields with many and diverse'types of equipment. Most of the systems for temperature control which have been used extensively in the past are expensive, heavy and consume large amounts of fuel or electrical power. However, the advent of the space age has brought changed design requirements for temperature control systems, particularly those used for space vehicles. Spacecraft systems for controlling temperature must be lightweight, with requirements for electrical power minimized as much as possible.

A specific problem relating to temperature control in spacecraft is that one side of the craft may be in direct sun light while the opposite side is shaded. This causes overheating on one side of the craft and creates a requirement for balancing the skin temperature over the whole surface of the spacecraft. This was accomplished during the recent Apollo 8 trip to the moon and around the moon by slowly rotating the spacecraft around an axis perpendicular to the suns rays so that all sides of the spacecraft were exposed to the sun light during a period of about an hour.

A specific problem relating to temperature control of spacecraft in earth orbit or in orbit around other planets is that the spacecraft is in daylight part of the time and darkness part of the time. This creates a requirement for dissipation of heat during the time the spacecraft is being heated by the suns rays and a requirement for heating the spacecraft while it is in darkness.

Some types of space equipment require a cover which provides isothermal or constant-temperature isothermal conditions. One type of space equipment requiring the latter type of cover is a space telescope. A space telescope is a precision optical instrument which must be protected from temperature change or temperature-differentials in its various parts. Its optical parts must be protected from damage. Furthermore, its metal parts must be protected from expansion or contraction caused by temperature extremes so that the focal length of the instrument does not change.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved cover for space equipment providing control of the temperature of the equipment.

A further object of the invention is to provide an improved cover for space equipment which is substantially isothermal, even when one side of the cover is being heated by sun light.

Yet another object of this invention is to provide an improved cover for space equipment which will efficiently maintain constant-temperature conditions for the equipment, even when the cover is exposed to variable temperature conditions, by providing a capability to store heat at times and return the stored heat to the system at other times.

These and other objects areaccomplished in the present invention which provides a double-wall enclosure, at least one container of fusible material mounted inside the enclosure, wicking material covering the interior surfaces of the enclosure and the exterior surfaces of each container and a heat transfer fluid contained within the enclosure. The fusible material acts as a thermal reservoir for storing heat, which is returned to the system when the heat is needed to maintain a constant-temperature condition in the cover. The heat transfer fluid and the wicking material enable the cover to act as a heat pipe in efficiently transferring heat from one side of the device to its other side or to the fusible material.

BRIEF DESCRIPTION OF THE DRAWINGS vention shown in FIG. 1.

FIG. 4 is an enlarged sectional view of the invention shown in FIG. 1, taken along line 4-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT With continued reference to the accompanying FIGS. wherein like numerals designate similar parts throughout the various views and with initial attention directed to FIG. I, there is illustrated a typical embodiment of the invention in the form of an isothermal barrel for a space telescope, designated generally by the numeral 10. The barrel 10 comprises a double-wall cylindrical enclosure having an outer wall 12 and inner wall 14 and two end walls 16, all of which enclose a cavity 17. Mounted within the cavity 17 of barrel 10 are one or, more enclosed containers 18 of a fusible material 20, which, for example, may be octocosane or another hydrocarbon of the paraffin series. These substances were chosen for this purpose because they have melting points in the range of F to 200 F, and a relatively high heat of fusion, which gives them good heat storage capabilities. In practicing the present invention a particular paraffin which has a melting material 22, which may be -300 mesh screen, or anumber of other known wicking materials. As may be seen in FIG. 2, the enclosed cavity 17 formed by the walls 12 and 14 and ends 16 of the space telescope contains a heat transfer fluid 24, whichmay be water, freon, alcohol or a number of other substances which are easily vaporized. The construction of the space telescope barrel 10 with its interior surfaces covered with the wicking material 22 and-with the cavity of the barrel 10 containing heat transfer fluid 24 enables the space telescope barrel 10 to function as one large heat pipe so as to utilize the latent heat of vaporization of the working fluid to transfer heat from one side of the barrel 10 to its other side, in accordance with known principles of operation of a heat pipe.

As may be seen in FIGS. 1 to 4, the metal outer wall 12 of the space telescope barrel 10 may be covered by a thin thermal coating 32. Depending upon the mission of the particular space equipment involved, the environment involved and the desires of the user, coating 32 may have either heat absorbing or heat reflecting characteristics, combined with either high or low emissitivity properties. The absorptivity (a) of the coating is chosen on the basis of the predominant solar wavelength of 0.6 microns, while the emissitivity (e) aspect of the coating is based upon the designed temperature ofoperation, considering all heat sources and sink temperatures within the environment. ale ratios are thus temperatures dependent and can be greater or less than 1. Thermal coatings which may be used as a part of the invention are already known. Since they may take various forms and are not considered novel per se, they will not be described in detail herein.

Containers 18 are constrained and supported by ends 16 and by standoffs or struts 26. Struts 26 may be seen in the open end view of telescope barrel shown in FIG. 2. Struts 26 serve the function of helping to support containers 18 in a position midway between outer wall 12 and inner wall 14, so that containers 18 are spaced from, and do not touch, walls 12 and 14. Struts 26 may be fabricated of wicking material 22, or, if they are required to carry a substantial portion of the weight of containers 18, they may also be made of any desired rigid structure and covered by wicking material 22. An additional function required of struts 26 is to furnish free communication for the coolant from inner wall 14 to outer wall. 12. On the outside of inner wall 14 are several heaters 28, which may be of the electrical calrod type, or other known types. FIGS. 3 and 4 show additional details of the interior construction of this embodiment of the invention.

One cycle of operation of the isothermal space telescope barrel it) follows:

When the sun light heats the outer wall 12 of space telescope barrel 10, the heat is absorbed by outer wall 12 and conducted to the inside of outer wall 12. There heat transfer fluid 24 absorbs heat and is vaporized. The vapor 30 then moves under vapor pressure through the cavity 17 of barrel 10 between and around containers 18 to the opposite (shaded) side of the interior cavity 17 of spacecraft barrel 10. The vapor 30 then condenses back to fluid 24 and forms drops of fluid 24 on wicking material 22 positioned on the inner sides of the walls 12 and 14, ends 16 and the outer walls of cans l8 and struts 26. The fluid 24 (condensate) then moves by means of capillary flow through the wicking material 22 back to the sunny side of outer wall12 where it absorbs more heat and starts the cycle over. In condensing, vapor 30 gives up heat which is absorbed by walls 12 and 1 4,ends l6 and containers 18. Thus heat is distributed evenly and practically instantaneo'usly to all parts of the surfaces of walls 12 and 14 and ends 16 so as to maintain spacecraft barrel 10 substantially isothermal.

During the time spacecraft barrel 10 is transferring heat from its heated side to its cold side, as described above, fusible material contained in containers 18 is absorbing heat and changing from the solid to the liquidstate. Thus, each container l8 acts as a thermal reservoir by absorbing heat. Then, whenever the heated spacecraft barrel 10 passes into darkness or otherwise enters a colder environment, fusible material 20 may change back to the solid state and give off heat which is returned to the system to efficiently and economically maintain it in a substantially constant-temperature condition, regardless of the source of the input energy, as long as the fusible material remains partially in the liquid state and partially in the solid state. Of course, if the fusible material becomes completely liquid or completely solid, then the isothermal temperature may rise or fall. if the system should need additional heat to maintain it at a substantially constant temperature, heaters 28 may be used with an onboard power supply (not shown) to produce heat as needed.

The invention disclosed herein may be modified so that it can be used as a heater attached to another space vehicle which requires heat but is .unable to maintain its longitudinal axis normal to the rays of the sun. This space vehicle heater" can have its longitudinalaxis normal to the craft to be heated and substantially normal to the rays of the sun. Vapor from the heater is pipedinto the heated craft, which may itself be a double-walled heat pipe. The latter craft is heated by the latent heat of vaporization released by condensation of the vapor piped in. The condensate is then wicked back to the heater device through piping. Thermal coatings and shutters may be used as desired, on both the heater and the heated craft, to minimize heat'losses to, the environment.

From the foregoing it may be seen that applicant has invented a novel type of constant-temperature isothermal spacecraft cover, one application of which is as a barrel for a space telescopeThe doublewall, heat pipe construction of this invention could have made the rotation of spacecraft, as

discussed under Description of the Prior Art above, unnecessary. The invention preferably includes thermal heat resersaid enclosure, for absorbing and storing heat energy and returning said heat energy to said enclosure when it is needed to maintain the temperature of said enclosure;

0. a heat transfer fluid contained within said enclosure, for

transferring heat froma first side of said enclosure to the opposite side of said enclosure;

d. wicking material covering the interior surfaces of said en-. closure and the exterior surfaces of each said container, for returning said heat transfer fluid from said opposite side of said enclosureto said first side of said enclosure, at

least one heater mounted on the outside surface of said inner wall, for maintaining said enclosure at a constant temperature.

2. The'isothermal cover for space equipment of claim 1 wherein said double-wall enclosure comprises:

a. an outer cylindricalwall;

b. an inner cylindrical wall;

0. two end walls connecting together walls at their opposite ends.

3. The isothermal cover for space equipment of claim 2 said outer and inner wherein each said container of fusible material is a closed container.

4. The isothermal cover forspace equipment of claim 3 comprising at least one strut contained within said enclosure, each said container of fusible material being mounted on said end walls and on at least one said strut.

s. The isothermal cover for. space equipment of claim 4 wherein each said strut comprises wicking material.

6. The isothermal cover for space equipment of claim 5 wherein a plurality of said containers of fusible material are" spaced equidistant around the circumference of the interiorcavity of said enclosure and are mounted midway between the said inner an and outer walls of said enclosure.

7. The isothermal cover for space equipment of claim 6 comprising at least one heater mounted on the outside surface of said inner cylindrical wall, for maintaining said enclosure at a constant temperature.

3. The isothermal cover for space equipment of claim 7 comprising a heat-absorbing coating applied to the outer surface of the said outer cylindrical wall.

9. The isothermal cover for space equipment of claim 7 comprising a, heat-reflecting coating applied to the outer sur-.

face of the said outer cylindricalwall.

10. The isothermal cover for space equipment of claim 8 wherein each said strut comprises a rigid structure having said wicking material as an outer cover.

11. The isothermal cover for space equipment of claim 9 wherein each said strut comprises a rigid structure having said wicking material as an outer cover. 

